pmTool is part of Activity Monitor, and kernel_task is the top level process in the OS, since it's the parent process of launchd, which is the parent process of everything else. I find that pmTool takes up a lot of memory when Activity Monitor is running for long periods of time, but closing and re-opening it should do the trick. As far as I know, the only thing to do about kernel_task is to restart.
ahh nice. yea i always have activity monitor up and running. thanks!